Multiturn potentiometer



Jan. 22, 1957 F. B. M LAREN MULTITURN POTENTIOMETER 2 Sheets-Sheet 1 Filed Aug. 11, 1954 1 JZZ;

m GNU Jan. 22, 1957 F. B. M LAREN MULTITURN POTENTIOMETER 2 Sheets-Sheet 2 Filed Aug. 11, 1954 MULTI'IURN POTENTIOME'IER Frederick E. MacLaren, Huntington, N. Y., assignor to Acton Laboratories, inc, Acton, Mass.

Application August 11, 1954, Serial No. 449,199

4 Claims. (ill. 201-56) The present invention relates to otentiometers, and more particularly to a multiturn potentiometer having a helical wire resistance element.

Heretofore multiturn potentiometers generally have employed a resistance element comprising a core, about which was wound in helical manner the resistance element. Such core and resistance Wire then was mounted in a helical groove either in or on the cylindrical support. Such construction has a disadvantage of not permitting the introduction of any correction after the helix is wound if it is found that the linearity does not meet certain standards. It, therefore, would be desirable to provide a different construction which Will provide a higher degree of accuracy. in accordance with the present invention this is accomplished by employing a self-supporting helical wire resistance element wherein each turn is individually secured into position by a suitable cement onto a drum support. In the application of the wire to the drum support a monitoring arrangement may be employed whereby it is possible to vary the distance between the turns of the helical resistance wire element, thereby to provide the desired degree of linearity.

It, therefore, is an object of the present invention to produce an improved multiturn potentiometer having a certain accuracy of linearity and resolution.

Another object of the invention is to provide an improved multiturn potentiometer having a low noise characteristic.

Another object of the invention is to provide a novel construction of a multiturn potentiometer.

Still another object of the invention is to provide an Improved multiturn potentiometer wherein the resistance element is a self-supported helix of wire.

A still further object of the invention is to provide an improved multiturn potentiometer wherein the individual turns of a self-supported helix of resistance wire are secured into position.

Still another object of the invention is to provide an improved multiturn potentiometer having novel means for limiting the number of turns of the actuating shaft.

Other and further objects of the invention subsequently will become apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

Figure 1 is a longitudinal cross-sectional view of a multiturn potentiometer constructed in accordance with the teachings of the present invention;

Figure 2 is a detail view of a portion of the construction of Figure 1;

Figure 3 is a longitudinal view of the device of Figure 1 shown with the cover in cross-section;

Figure 4 is a rear end view of the device shown in Figure 3;

Figure 5 is a detail view of a portion of the construction of Figures 1 and 3; and

Figure 6 is an enlarged view of a portion of Figure 3.

"Referring to the drawings, and more particularly to Figures 1 and 3, there is illustrated a multiturn potenatent tiometer having a support or base 11 comprising a hollow cylindrical portion 12 having an annular flange 13 which may be provided with a plurality of threaded openings 14 for receiving mounting screws when the flange 13 is positioned against a support or panel. The base 11 carries at one end a bearing 15 resting against a snap ring 16 mounted in an internal groove within the cylindricai portion 12. At the other end a similar bearing 17 is provided, which bears against a snap ring 18 fitted into an internal groove within the cylindrical portion E2. The bearings 15 and 17 carry a shaft 19 which at its front end is provided with an annular groove, into which is fitted a lock ring 21 hearing against the front surface of the bearing 15. At the other end the shaft 19 is provided with a sleeve 22 which is engaged by a resilient washer 23 bearing against an arm 24 fastened by a suitable clamp or set screw 25 to the end of the shaft 19. The arm 24 may be shifted angularly for proper phasing of the contact relative to the mechanical stops. From this it will be noted that the shaft 19 is now secured against longitudinal movement. The resilient washer 23 spring loads the bearings of shaft 19 to remove radial and end play.

Within the cylindrical portion 12 of the support structure 11 the shaft 19 is provided with a threaded portion which most conveniently is provided by a threaded sleeve 26 secured in position by two pins 27 and 28 which also serve as stop pins for a follower nut. The threaded sleeve 26 is provided with a follower nut 29 having a depending portion 31 provided with a longitudinal groove which engages a longitudinally arranged Wire guide 3i mounted on the inside of the cylindrical portion 12. The upper end of the follower nut 29 has two Wing portions 32 and 33 arranged to engage the pins 27 and 28 at either end of the limit of travel of the follower nut 29. The Wing portions 32 and 33 at the same time are arranged to engage stop pins 34 and 35 mounted on the inside of the cylindrical portion 12 for cooperation with the stop pins 27 and 28 carried by the shaft 19. The wing portions 32 and 33 by engaging the cooperative stop pins of the shaft and on the inside of the cylindrical portion 12 therefore limit the rotary motion of the shaft 19 Without unduly applying a binding force on the threads of the threaded sleeve 26.

The cylindrical support portion 12 carries a grooved drum 36 having a flange 37 hearing against the annular portion 13 of the support structure 11. The flange 37 may be provided with a plurality of openings, into which are fitted screws 38. The flange 37', as may be seen from Figures 3 and 4, carries a plurality of electrical terminals 41, 42 and 43. The construction of the terminals is readily apparent from Figure 1 wherein it will be noted that the terminal 42 has an axial opening 44 so that a wire may be inserted therein and solder applied for a positive connection. The terminal 42 has an insulating sleeve 45. The end of the terminal 42 likewise has a longitudinal bore 46, in which is connected a wire 47 which leads to a slip ring carried by an end plate 49 secured to the end of the support structure 12 by suitable screws 51. The end plate 49 also serves to hold in position the drum 36. The other terminals 41 and 43 make connections to the ends of the resistance element carried by the grooved drum 36.

It will be noted from the enlarged Figure 2 that the drum 36 has two parallel helical grooves 52 and 53. The groove 52 preferably has a square cross-section, whereas the groove 53 has a semi-circular configuration. The semi-circular cross-section groove 53 carries a selfsupporting helix of resistance wire 54 where the individual turns are retained in position by a cement 55.

It will be noted from Figures 1, 3, 5 and 6 that the arm 24 carries a guide member comprising two parallel rods 56 and 57 suitably spaced at their far ends by a spacing block 58. The arm 24 is provided with an electricallvinsulated terminal 59, from which extend two springs 61 and 62, shown in Figure 4, terminating in bent portions as indicated in Figure 1 to engage the slip ring 48. The electrical terminal 59' also. is connected all mechanical backlash between motion of the arm 24 and resilient electric contacts 68 and 69 and positively position the carriage 64.- The central portion 65 also carries two contact wires 68 and 69 having their terminal portions arranged to contact opposite sides of the helical wire element 54. It will be noted that each of the wire contacts 68and 69 has an oppositely extending portion 70 which rests in one of the grooves 52 as is apparent from Figures 3 and 5. Thus the carriage and the contacts are so constructed as to positively position the carriage with respect to a particular turn of the resistance wire helix 54. It has been found that this particular construction has greatly reduced theelectrical contact noise, which otherwise might be generated in the circuit by other types of contact constructions.

A suitable cover 71 engages the peripheral portion of the flange 37 of the drum 36, and is fastened by the screws 38.

From Figure 3 it will be noted that the flange 37 has an annular groove 72 which intersects countersunk portions 74 adjacent the terminals 41, 42 and 43. The annular groove 72 and countersunk portions 74 are filled with varnish when the cover is placed in position, and thus all extraneous matter issealed out.

While for the purpose of illustrating, and describing the present invention a particular embodiment has been illustrated in the drawings, itis to be understood that the invention is susceptible of certain variations falling within the spirit and scope of the invention set forth in the accompanying claims.

I claim as my invention:

1. A multiturn potentiometer comprising a cylindrical base, a shaft coaxially mounted therein, a drum carried by said base and having externally twoparallel helical grooves, a self-supporting helical resistancewirernounted in one ofsaid grooves, each turn of said wire being individually fixed in position in said groove, an arm carried at one end of said shaft, support means carried by the end of said arm parallel to the surface of said drum, a movable contact carriage slidably mounted on said support means, said carriage having a pair of Wire A. elements in engagement with said helical resistance wire, said wire elements each having a portion in engagement with said other groove, and means within said base for limiting the rotation of said shaft to a predetermined number of turns.

2. In a multiturn potentiometer, the combination comprising a support having a cylindrical portion, a shaft carried thereby, said shaft having a threaded portion Within said'cylindrical portion of said support, a stop pin carried by said shaft at each end of said threaded portion, a follower nut mounted on said threaded portion, a guide member for said nut carried by said support, stop'pins mounted within said support for cooperating with saidfirst stop pins, said follower nut at each end of its travel engaging a stop pin on said shaft and a stop pin on said support said cylindrical portion having two exterior parallel helical grooves, a wire resistance element mounted in one of said grooves, a contact assembly mounted from the end of said shaft including a wire contact member having two curved portions engaging two convolutions of said other groove and having two resilient end portions for engaging the helical resistance element on'two angularly spaced points.

3. In a helical 'multiturn potentiometer having a support cylinder having two parallel helical grooves with a helical wire resistance element mounted in one of said grooves, a movable contactassembly including an insulator body member, a-wire contact member carried by said body member and consisting of wire having an intermediate portion for engagement with the other of said grooves, said contact member having two resilient ends arranged with an angle therebetween whereby said resilient ends engage the helical convolutions of said resistance wire at spaced points.

References Cited in the file of this patent UNITED STATES PATENTS 1,657,670 Fitch Jan; 31, 1928 2,101,830 Babcock Dec. 14; 1937 2,371,159 Erb Mar. 13, 1945' 2,442,469 Palya June 1, 1948 2,473,048 Beckman June 14, 1949' 2,665,355 Van Alen et a1 J an. 5, 1954 

